Some conventional resistive random access memory (RRAM) elements, including some CBRAM type elements, include a switching material formed between two electrodes, such as an anode and a cathode. Some conventional anode materials will oxidize when subject to an environment containing oxygen, such as air. Oxidation of an anode can increase its resistance or even prevent a conductive connection from being made to the memory element.
Conventionally, to prevent oxidation of an anode, a conductive “cap” layer can be formed over an anode to prevent it from oxidizing. In architectures that include a common conductive connection among multiple elements (e.g., a plate), a conductive cap can also advantageously decrease a resistance of the plate.
It can be desirable for the materials of RRAM/CBRAM elements to be compatible with existing CMOS fabrication processes. In particular, RRAM/CBRAM elements should be able to withstand anneals of at least 400° C. Preferably, materials of an RRAM/CBRAM can include those already used in a fabrication process. As a result, titanium nitride (TiN) or tantalum nitride (TaN) are used for a cap layer.
FIG. 13 is a side cross sectional view of a conventional element 1301. Element 1301 can include a cathode 1303, a switching layer 1305, an anode layer 1307 and a cap layer 1309. If a cap layer 1309 is formed from a material such as TiN or TaN, columnar grain structures can be formed, resulting in grain boundaries 1311 that can extend through the cap layer 1309 to the anode layer 1307. Such grain boundaries 1311 can allow oxygen and/or other contaminants from an atmosphere to penetrate down to material of the anode layer 1307. Grain boundaries (e.g., 1311′) may be particularly problematic at locations in the cap layer 1309 corresponding to the corner of the cathode 1303, where a step might occur.